DE3518603A1 - IMAGE DEVICE WORKING WITH CORE MAGNETIC RESONANCE - Google Patents

Description

Henkel, Feiler, Hänzel & Partner

Patent attorneys

Yokogawa Hokushin Electric Corporation

and

Yokogawa Medical Systems, Ltd. Musashino-shi, Tokyo, Japan

33 '

FA 85101 / wa

Imaging device working with nuclear magnetic resonance

Imaging device working with nuclear magnetic resonance

The invention relates to a so-called NMR imaging device for working with nuclear magnetic resonance medical equipment for determining the distribution of certain atomic nuclei or the like. in an examination subject from its outside using the

nuclear magnetic resonance phenomenon or so-called NMR-15

Appearance.

In the case of an NMR imaging device, an image of the interior becomes of an examination subject obtained in that the examination subject in magnetic fields that are generated by supply

an electric current to a coil for the generation of static magnetic fields and by supplying electric Current with high frequency to a high frequency coil for the application of the examination subject

with high frequency magnetic fields below a predetermined one 25th

Angles are generated, introduced and the resulting NMR appearance in the examination subject by means of an electronic computer is processed or evaluated. Here it is necessary to adjust the intensity of static electric fields is constant

hold for a satisfactory NMR image. With a water-cooled normal conducting four-coil magnet for the generation of static magnetic fields For example, the current supplied to the coils for generating the static magnetic fields by means of a

Constant current source maintained at a predetermined size.

Even with the arrangement of such a device, if the temperature of the coils changes, the temperature of the frame for supporting the coils, the

Ambient air temperature, the temperature of the cooling water for the coils and / or the amount of cooling water, the temperatures of the coils and their support frame are appropriate Changes so that the intensity of the static magnetic fields due to deformation of the coils and the like. fluctuates due to thermal expansion and thereby deteriorates the NMR image.

The object of the invention is thus to create a working with nuclear magnetic resonance or NMR imaging

training device, in which a deformation of coils or the like. caused by thermal expansion Deterioration of an NMR image can be corrected automatically.

The solution to this problem results from the features characterized in the patent claim.

In the following, preferred embodiments of the invention are explained in more detail with reference to the drawing. It demonstrate:

Fig. 1 is a schematic representation of a device according to the invention,

^ö FIG. 2 is an enlarged view of the magnetic coils and the like, seen in the direction of the arrow A in FIG. 1,

3 and 4 are schematic representations of devices for indirect measurement of temperature

of the solenoids based on their resistance value and

Fig. 5 is a block diagram of another embodiment for control or adjustment in the NMR imaging apparatus according to the invention.

The embodiment shown in FIG. 1 contains 10

Magnet coils 1 for generating static magnetic fields. Although four magnet coils 1 are shown in FIG. 1, the invention is in no way restricted to this number. Each magnetic coil 1 consists of numerous turns of conductor wires made of, for example, copper. The four

Magnet coils 1 are electrically connected in series with one another, but they can also be connected in parallel. Although not shown in more detail in Fig. 1, the circumference of each solenoid 1 with cooling water becomes theirs Cooling charged. At 3 are frames to hold the

Magnet coils 1 indicated. Viewed in the direction of arrow A in Fig. 1, the frames are 3 and the solenoids 1 arranged in the manner shown in FIG. In particular, each solenoid 1 has an annular shape Shape, with four such solenoids 1 from the

Frame 3, to be worn. While each solenoid 1 has an annular shape, the shape of the frame 3 is not limited to the shape shown in Fig. 2, rather, it can also be circular, for example. The digits 5-9 denote items to be described in more detail

Coefficient units that or the like depending on the temperature coefficient. the solenoids 1 and the frame 3 can be adjusted. Temperature measuring units 11-16 are used to measure the temperature on the respective locations of these measuring units according to

Fig. 1. In particular, the measuring units 11-14 measure

the temperature of the individual magnet coils, the measuring unit 15, the temperature of the frame 3 and the measuring unit

16 is the atmosphere or ambient air temperature. These 5

Measuring units are known per se. An adder / subtracter 17 is used to add / subtract through signals input to each of the coefficient units 5-9. A power source 19 is used to feed the individual solenoids 1 with electric current below

Adjustment of the magnitude of the current I on the basis of the signal from the adder / subtracter 17 and one more reference voltage to be described 20.

In Fig. 1, the letters a denote a tem-

temperature of the cooling water for the solenoid coils and b a signal related to the amount of cooling water Signal. The signal a is via the coefficient unit 6, the water quantity signal b via the coefficient unit 5 fed to the adder / subtracter 17. the

Reference voltage 20 is used to set the current I to be fed into the coils.

The device according to Fig. 1 works as follows:

If in one embodiment of the NMR imaging device for medical equipment, if the average temperature of the solenoids increases by 1 "C, the temperatures decrease Magnetic fields in the central area of the magnet coils due to the thermal expansion of the copper that forms the coils

material by about 21 ppm. With a temperature increase of 1 ^° C. at the frame 3, the distance between the magnet coils 1 increases accordingly due to the thermal expansion of the frame 3, which results in a reduction in the magnetic fields in the central area of the magnet coils 1

gives about 75 ppm. An examination object is in the

arranged by the arrangement of the four magnet coils 1 formed cylindrical space. If the

Magnet coils 1 with a constant current I from the 5th

Power source 19 are charged here, are inside of the cylindrical space generates static magnetic fields.

According to the invention, the temperature measuring units 11 are 15 arranged on the respective magnet coils 1 and the frame 3 and on sizes or values according to the Temperature coefficients of the solenoids 1 and the frame 3 are set (so that the measurement results on the Units with larger temperature coefficients

those for the units nt smaller temperature -15

coefficients can be matched). The output signals of the temperature measurement units are taken from the coefficient units 7, 8, and their addition size is used to control the current source 19. The current I can therefore according to the

Changes in temperature of the magnet coils and / or the frame can be adjusted so that fluctuations in the magnetic field H _{n are} suppressed. If, in particular, the magnetic field H acting on the examination object tries to vary due to the change in temperature

is, the examination subject can be adjusted by setting the The magnitude of the current I fed into the magnet coils is acted upon by magnetic fields of constant intensity will.

Since the temperature of the Rannen 3 under the influence

the ambient temperature changes, the latter can be measured instead of the temperature of the frames 3, like this indicated by the temperature measuring unit 16 according to FIG that can be used for correction. 35

BATH

Since the temperature of the magnet coils 1 is influenced by the cooling water temperature, the cooling water quantity,

Ambient temperature and amount of air flow 5

is subject, these variables can also be used for the correction, as indicated at a, b in FIG.

In addition, since the temperature of the individual sections of the magnet coils is not always uniform, must several temperature measuring units can be arranged at the relevant sections.

Instead of the different temperature units of measurement too

can use, as shown in Fig. 3 or 4, the change 15

the electrical resistance of the solenoid coils

be measured by means of appropriate devices, the measured value for the correction as the average temperature of the magnet coils, based on the temperature coefficient known electrical resistance, 20

can be used.

Fig. 3 illustrates a solenoid 1, a shunt resistor 20 and a divider 21. If the input signals of the divider to el and e2 are assumed 25th

the output signal eO from the divider 21 indicates the resistance of the magnetic coil 1, i.e. eO = e1 / e2.

According to FIG. 4, resistors 22-24 and a magnetic coil 1 form a (measuring) bridge circuit, a span 30

voltage via the measuring bridge sides is accepted by an amplifier. The output signal eO of the amplifier 25 shows the fluctuations in the resistance value of the magnetic coil 1.

Fig. 1 illustrates an arrangement in which all

factors mentioned are taken into account, i.e. temperature measurement on the magnet coils (units 11 - 14),

Temperature measurement ah frame 3 (unit 15), cooling 5

water temperature measurement (unit a), cooling water quantity measurement (unit b) and ambient air temperature measurement (Unit 16). Because here the deviations between the temperature coefficients for the individual sections

by means of the respective coefficient units 5-9 10

are adjustable, the adder / subtracter 17 is for Adding and subtracting the sizes or values from the respective coefficient units are provided.

However, it is not in every case for the invention

necessary all these parameters to adjust the current Rather, the current I can be detected on the basis of at least one of the aforementioned measured parameters are set, which largely solve the problems in the prior art outlined at the beginning

permit. This means that it is only necessary according to the invention is to record at least one of the parameters mentioned for setting the current I.

Above is an embodiment with reference to FIG

describes at which the current I as a function of temperature changes at the individual sections and is adjusted by the change in the amount of cooling water, so that undesirable effects of this Changes to the NMR image can be corrected.

In the following, with reference to FIG. 5, another control or setting device for correcting undesired Effects or influences of the temperature fluctuation at the individual sections on the NMR image

wrote.

Figure 5 shows a complete block diagram of an NMR imaging apparatus. The arrangement of Fig. 5 comprises

a device 5 generating a static magnetic field

30 from the same magnetic coils, frames and the like. As in Fig. 1, the magnetic fields H as static magnetic fields generated, as well as high-frequency coils 31 and 32. The high-frequency coils 31, 32, not shown in FIG are indispensable for an NMR imaging device. The high frequency magnetic fields generated by the high frequency coils are designed so that they form a predetermined angle relative to the static magnetic fields H determine. With 33 and 34 are high frequency amplifiers

denotes, of which the amplifier 33 for application 15

a current of an appropriate size to the radio frequency coil 31 is used, while the amplifier 34 is a for the NMR phenomenon detected by the high frequency coil 32 amplifies the relevant signal and transmits the amplified signal to the next stage. The order

further comprises a high frequency oscillator 35, one Multiplier circuit 36, analog / digital or A / D converter 37 and 38 for converting analog signals into digital signals and an (electronic) computer 39, the

those on the NMR phenomenon in each section of the sub-25

object-related data from the A / D converter 3 7 decreases and based on it the interior of the object to be examined outputs representational image data. Numeral 40 denotes a display unit such as one

Cathode ray tube, while with B a device for the 30th

Measurement of various types of parameters already explained with reference to Fig. 1 (e.g. temperature of the magnet coils, the frame, the cooling water, etc.) is designated.

In the arrangement of FIG. 5 are for a usual

In addition to the measuring device B, the NMR imaging device also uses other structural units. Since the fundamental

Operation of the device according to FIG. 5 (as NMR-Abbil-5

processing device) is known per se, it only needs to be explained briefly below.

It is known that the (atomic) nuclei (whose atomic or mass number is odd) in static magnetic fields H ^υ

subject to precession, and the nuclear magnetic resonance or NMR frequency (Larmor frequency) Ca _n to

O ₀ = f-

determined and therefore proportional to the static magnetic fields H. is. In the above equation, γ ″ stands for the gyromagnetic ratio as the type of nuclei Constant. By detecting the temperature of the

Magnet coils or the like. by means of the device B according to FIG. 5 and thus correcting the high frequency O of the high frequency oscillator 35 with y · ^ H corresponding to the temperature fluctuation ^ H of the static magnetic field H _Q

Any effects of fluctuations in the 25th

Magnetic field intensity H on the NMR picture reduced will.

Optionally, the signals for the means of the device B detected temperature of the solenoids and the like.

by the A / D converter 38 of an analog / digital conversion are subjected and entered into the computer 39 as data. Then a mathematical one is generated by the computer 3 9 Operation for shifting the Fourier spectrum of that detected by means of the high frequency coil 32

High frequency signal carried by y · ^ H, whereby the

The effect of the fluctuations in the magnetic field _{intensity H n} on the NMR image can also be reduced.

Since in the invention, as described above, means for compensating for the deterioration of the NMR image are provided by fluctuations in the intensity of the static magnetic fields H due to Changes in the temperature of the solenoid coils, the temperature

temperature of the frame for holding the magnet coils and the temperature of the cooling water for the magnet coils as well the amount of cooling water and the like. Caused, by changing the specified parameters that of it resulting undesirable effects or influences

be reduced to a minimum.

Claims (1)

Claim Nuclear magnetic resonance imaging apparatus for obtaining an image of the interior of a Object to be examined by introducing the latter into by feeding a first coil with an electrical 10 Electricity generated magnetic fields, supply of an electric one High-frequency current to a second coil for the purpose of applying high-frequency magnetic fields to the examination subject at a predetermined angle and mathematical processing of the nuclear magnetic resonance phenomenon occurring in the object by means of an (electronic) computer, thereby characterized in that at least the temperature of the first coil, the temperature of a holding the first coil Frame, the ambient air temperature, the temperature of the cooling water for the first coil and / or the amount of cooling water can be detected or measured and one Deterioration of the image of the examination subject using at least one of the following devices can be compensated: a) Means for controlling the intensity of the generated Magnetic fields by correcting the magnitude of the current supplied to the first coil based on the measurand; b) Means for correcting the high frequency on the Basis of the measurand; and c) Means for mathematically correcting a generated by the imaging device in the computer nuclear magnetic resonance image based on the Measurand.
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